Problem 25.78 Compact fluorescent bulbs are much more efficient at producing lig

Question

Problem 25.78

Compact fluorescent bulbs are much more efficient at producing light than are ordinary incandescent bulbs. They initially cost much more, but last far longer and use much less electricity. According to one study of these bulbs, a compact bulb that produces as much light as a 100W incandescent bulb uses only 23.0W of power. The compact bulb lasts 1.00Ý104 hours, on the average, and costs $ 11.0 , whereas the incandescent bulb costs only 74.0 ¢, but lasts just 750 hours. The study assumed that electricity cost 8.00 ¢ per kWh and that the bulbs were on for 4.0 h per day.

Part A

What is the total cost (including the price of the bulbs) to run incandescent bulbs for 3.0 years?

............... dollar(s)

Part B

What is the total cost (including the price of the bulbs) to run compact fluorescent bulbs for 3.0 years?

.............   dollar(s)

Part C

How much do you save over 3.0 years if you use a compact fluorescent bulb instead of an incandescent bulb?

............. dollar(s)

Part D

What is the resistance of a "100 W" fluorescent bulb? (Remember, it actually uses only 23 W of power and operates across 120 V.)

Explanation / Answer

a)

Total Hours incandescent bubl is on for 3 years

T=3*4*365==4380 hours

but each bulb will be working for 750 hours

Number of bulbs needed is

N=4380/750 =6 bulbs

Energy Consumed by incandescent bubls for 3 years is

E=(100/1000)*4*(3*365) =438 KWH

Cost=438*(8/100)+6*(74/100)=$39.48

b)

Energy consumed by flourscent bulbs for 3 years is

E=(23/1000)*4*(3*365)=100.74 KWH

Cost =100.74*(8/1000)+11=$19.06

c)

Money saved =39.48-19.06 =$20.42

d)

Resistance of flourscent bubl is

R=V2/P =1202/23

R=626 ohms

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